For improving the luminance efficiency, the prior light emitting diode usually includes a reflective layer. As shown in FIG. 1, an n-type semiconductor layer 104, an active layer 106 and a p-type semiconductor 108 are formed successively on a transparent substrate 102. The light generated from the active layer 106 is emitted through the transparent substrate 102 into the air. To improve luminance, the light toward p-type semiconductor 108 needs to be reflected and radiated out through the substrate 102. Typically, the material of the reflective layer 116 is selected from metals with high reflectivity, such as Ag, Au or Al. This configuration has been disclosed in U.S. Pat. Nos. 6,794,690 and 6,812,502 and U.S. Publication No. 2004/0182914.
However, peelings may occur between the reflective layer 116 and the p-type semiconductor 108 during a lift-off step due to poor adhesion between the metal layer and the p-type semiconductor 108.
In addition, when the reflective layer is made of Ag, there arises a current leakage problem that are caused by migration of silver, and therefore performance of the light emitting diode is lowered.
Current spreading is important to luminance and uniformity of the light emitting diode. Since the current is from the p-type semiconductor layer 108 to the active layer 106 for generating light, the current spreading in the p-type semiconductor layer 108 is a significant factor for good luminance efficiency. Accordingly, the current spreading has to be improved for high luminance efficiency.
Therefore, there is a need to provide a light emitting diode and its fabricating method to enhance the adhesion between the metal reflective layer and the p-type semiconductor layer, and furthermore to improve luminance and performance of the light emitting diode.